I think I messed up

I let go of a person I was really close to a few months ago. I felt like our interactions were not the same anymore, I felt like he would ditch me for his new friends often, and he did. That much I know is true. It got to the point where he stopped apologizing for missing things that he would not miss before. We started talking less and less and at some point it felt like he would only come to me when he needed something. My friend who I could come to with any problem with full confidence that we could solve it together started to treat me like a nuisance. It felt like that's how it was. I thought about leaving for months before I decided to actually do it. He contacted me some time after and tried to apologise, said he didn't know that he was on his last chance, I wonder if he would have behaved differently if he did know. He asked how he could make amends and I didn't allow it. At the time I thought I was doing something really good for myself, not allowing anyone to walk all over me, putting my mental health over everything else. But this has harmed me more than anything.

Since then, I've depressive episodes more often than I usually would. I relapsed in many ways and I still think about it today. If things would have been different if I heard him out, if I jumped into abandoning him before he abandoned me. When he asked how he could fix it and I refused, he didn't fight me on it. I thought that was a sure sign that he got tired of me too, the apology and all that was just a formality and he must have been happy to get rid of me. Today though, I don't really know. I looked through our texts and we talked a lot more towards the end than I thought we did. I thought it took him a really long time to notice that I was gone but he noticed fairly quickly. I feel like I don't know anything about this situation now and I might have messed up the only friendship that I believed would really last. He made me feel expendable but I also want my friend back and I don't know what to do because nothing makes sense anymore.

I'm posting here because I've suspected that I have BPD for a while now and the person I'm talking about had it too and noticed signs in me too. There were times when he would mention that I seemed borderline too but I thought about how I don't really do anything even remotely risky, I'm not going out looking for my next sexual conquest or trying hard to keep people in my life. I let them go and maybe would be sad about it for a few days and then move on. Moving on would usually involve looking for other friends. Im looking now and no one can replace him. There are parts of me that only he had access to.